Data storage is an important aspect of today""s information technology. A great deal of effort has been made by the storage industry to increase the real data density of a storage medium in order to meet the ever increasing demand for higher capacity storage devices.
Magnetic storage devices such as fixed or removable magnetic disks and tapes are widely-used conventional storage devices. Optical storage devices, such as CD-ROMs, are emerging as an alternative technology to the conventional magnetic technology because of their potential for high-density data storage.
Magneto-optical (xe2x80x9cMOxe2x80x9d) drives use both magnetic and optical effects to read and write data. MO disks are typically plastic or glass disks coated with a layer of a material with special magnetic properties. This layer of magnetic material, typically a rare earth-transition metal compound such as TbFeCo, serves as an active layer for storing data. The active layer may be covered with an optically transparent protective layer.
To write data to the MO disk, a high intensity laser is used to heat the material up to its Curie point, allowing its magnetization to be altered by a magnetic write head including a biasing coil, and then xe2x80x9cfrozenxe2x80x9d in the (altered) magnetic state as region cools.
The MO driver may be a far-field system in which the read/write head, including optics for focusing the laser and the magnetic coil, is kept within a fixed distance from the media by a focus servo system. Alternatively, the MO driver may be a near-field system in which the read/write head is kept very close to the media, for example, using a xe2x80x9cflyingxe2x80x9d head configuration similar to the Winchester design used in hard disk drives. Regardless of the type of configuration, the magnetic coil must be close enough to the media to generate enough magnetic field in the recording layer.
In an embodiment, a driver in a far-field magneto-optical (xe2x80x9cMOxe2x80x9d) system has a read/write head that includes an objective lens for focusing a laser beam onto an MO disk. The objective lens is housed in an objective lens holder. A magnetic biasing coil is mounted to the bottom of the objective lens holder, between the objective lens and the MO disk. The coil includes an aperture to allow the laser beam to pass through the coil and onto a surface of the disk. The coil may generate a modulated magnetic field for writing data to the MO disk in a single pass.
he objective lens holder is moved up and down as the disk spins by an actuator to maintain the laser beam in focus on the MO disk surface. The actuator is controlled by a focus servo system including an optical feedback system. The focusing operation maintains the objective lens and the coil precisely at predetermined distances from the MO disk surface, despite irregularities in the disk and disk wobble.
Since the coil remains near the surface of the MO disk (e.g., between about 5 and 50 microns), the coil may be relatively small, allowing it to switch at high speeds. For example, the coil may have an inner diameter of about 90 microns and generate a field of about 1 Oe/mA.